The present invention relates to a light scattering particle size distribution measuring apparatus, which irradiates a material sample with light from a light source, and measures the size distribution of particles in the sample on the basis of a scattered light intensity pattern obtained thereat.
Systems capable of measuring the size distribution of particles within a sample of material are useful in a plurality of fields. FIG. 7 shows a schematic of a prior art scattering particle size distribution measuring apparatus system. As shown in FIG. 7, the system comprises a light source 71, capable of emitting laser light 72. In addition, a shutter 73, comprising a shutter member 73a and a shutter driving member 73b, is used to modulate the laser light 72. A beam expander 74 expands the laser light 72 prior to incurring a flow through cell 75 containing a material sample 76. Thereafter, a condenser lens 77 is used to focus the light onto a photodetector 78 which detects the scattered and transmitted light from the condensor lens 77. Commonly, a multiplexer 79, which is in communication with a CPU 80, captures the signal from the photodetector 78 upon the detection of light. The CPU 80 may be programmed with various algorithms and other mathematical formulae to permit arithmetic computations of scattering based on the light intensity pattern received at the photodetector 78. A personal computer 81, in communication with a display terminal 82, may be used to control the overall system.
In the foregoing system, when a cell 75 containing a material sample 76 is irradiated with laser light 72, a portion of light is scattered by particles within the material sample 76, and a portion of the light is transmitted through the material without a scattering effect.
A problem associated with prior art systems requires the optical axis of a photodetector 78 be held exactly coincident with that of a light source 71. More specifically, the center of an axis of laser light 72 emitted from a light source 71 is required to be coincident with a center of a light receiving device of the photodetector 78. Commonly, the foregoing axis become misaligned due to the thermal deformation of the light source 71, the thermal deformation of the optical bench, thermal deformations in the cell 75, condenser lens 76, or photodetector 78.
In an effort to correct the foregoing misalignment issues, conventional particle size distribution measuring systems having utilized optical stages 83, commonly referred to as X-Y stages, to maintain the optical axis. As shown in FIG. 7, the X-Y stage moves a photodetector 78 in parallel, and corrects the foregoing misalignment of the optical axis. To correct a misalignment, the operator is required to manually actuate the direct acting actuator 85, to correct misalignment along the X axis, or the direct acting actuator 84, to correct a misalignment along the Y axis. Generally, the direct acting actuators 84 and 85, respectively, having included piezoelectric devices or a stepping motor.
The above-referenced optical axis adjustment work is required to be performed for every measurement and takes several minutes for each adjustment. As such, it has been required for an operator to expend considerable time and effort for each measurement. In addition, inaccurate measurements could occur should there be a time lag between the optical axis adjustment work and the measuring operation due to a plurality of factors, such as, for example, vibrations, changes in temperature, or other environmental conditions.
The present invention has been made in view of the foregoing matters, and an object of the present invention is to provide a light scattering particle size distribution measuring apparatus which does not require a burdensome optical axis adjustment of operator for every measurement, thereby maintaining a state most suitable for measuring.
To achieve the above object, the present invention discloses a light scattering particle size distribution measuring apparatus which irradiates a sample with light from a light source, detects the resulting scattered light from the sample by a photodetector, and measures the size distribution of particles in the sample on the basis of a scattered light intensity pattern obtained. More specifically, the present invention comprises an automatic adjustment mechanism which aligns and maintains a central position of the foregoing photodetector with a central position of the foregoing light source is provided.
In another embodiment, a light scattering particle size distribution measuring apparatus is provided comprising an optical axis adjustment mechanism capable of automatically adjusting the central positions of the light source and the photodetector in a state most suitable for measuring. The system monitors the quantity of light antecedent to irradiating a sample and quantity of light on a photodetector after irradiating a sample, and adjusts the position of a light source, the photodetector, or an optical device positioned between the light source and the photodetector.
In yet another embodiment, the present invention discloses a light scattering particle size distribution measuring apparatus capable of holding the control data antecedent to the decrease of the quantity of light when the quantity of light on a photodetector is significantly lowered compared with the quantity of light antecedent to irradiating a sample by monitoring the quantity of light antecedent to irradiating a sample and the quantity of light on a photodetector. In addition, the present embodiment is capable of retrieving the optimal positions of various optical components in a range, thereby automatically controlling the quantity of light on a photodetector.
In the light scattering particle size distribution measuring apparatus having the constitution described above, an automatic adjustment mechanism aligns the central position of the photodetector with the central position of the light source. The optical axis adjustment, which, conventionally was required to be manually performed by the operator, or through a control software stored on the personal computer, before measuring the particle size, becomes unnecessary. It is, therefore, possible to reduce the time required for each measurement, such as preparatory work before measuring. In addition, the present system is capable of always measuring in optimal conditions, thereby consistently achieving a particle size distribution measurement having a high degree of measuring precision.